Regular exercise has important health and economic benefits. Wellness programs, including initiatives that target exercise, are prevalent among employers that offer health insurance. Provisions within the Patient Protection and Affordable Care Act are expected to increase further the diffusion of employer-based wellness programs. Yet, there is a limited evidence base to inform employer decision-making about how to design or target these programs to maximize their effectiveness for influencing individuals' initiation and maintenance of exercise. The proposed multidisciplinary project will examine the effect of the Fitness Rewards Program (FRP), an incentive-based wellness initiative, launched by the University of Minnesota in 2008, to promote exercise behavior. Using three years of administrative data and rigorous analytic methods, this research contributes in four ways to our understanding of the effectiveness of incentive-based strategies on exercise behavior. First, through a theoretically-grounded analysis of individuals' monthly exercise behavior, the research will utilize detailed information on individuals' demographics, health status, and health beliefs to identify and differentiate the factors that affect the initiation of behavior from thosethat affect maintenance, an issue relatively unexplored. Second, this study will generate insights into the types of intervention strategies that augment motivation to initiate and maintain health behaviors that contribute to the reduction of risk for certain chronic and acute conditions. Third, by examining how behavioral responses to the incentive differ by individuals' characteristics, our results will inform decisions regarding which groups to target when implementing incentive-based strategies to promote the initiation and maintenance of exercise. Finally, by focusing on a large, diverse employer-based population, our analyses will generate insights regarding the behavioral responses of individuals under conditions that reflect the actual environment in which most incentive-based programs are being implemented. Results from this study will generate evidence that employers and researchers can use to inform decision-making about the design, implementation, and evaluation of incentive-based, wellness programs -- including decisions about participation, exercise frequency requirements, facility access, and incentive structure.